Method for fabricating metal gate devices and resulting structures

ABSTRACT

A method for fabricating a semiconductor component includes forming an interlayer dielectric (ILD) layer on a substrate, forming a trench in the interlayer dielectric layer, forming a metal gate in the trench, removing a portion of the metal gate protruding from the ILD layer, reacting a reducing gas with the metal gate, and removing a top portion of the metal gate.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/050,687, filed Jul. 31, 2018, which is a divisional of U.S. patentapplication Ser. No. 14/831,409, filed Aug. 20, 2015, now U.S. Pat. No.10,090,396, issued Oct. 2, 2018, which claims priority to U.S.Provisional Application No. 62/194,736, filed Jul. 20, 2015, which areherein incorporated by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. The smaller featuresize is the use of multigate devices such as fin field effect transistor(FinFET) devices. FinFETs are so called because a gate is formed on andaround a “fin” that extends from the substrate. As the term isimplemented in the present disclosure, a FinFET device is any fin-based,multigate transistor. FinFET devices may allow for shrinking the gatewidth of device while providing a gate on the sides and/or top of thefin including the channel region. Another advancement implemented astechnology nodes shrink, in some IC designs, has been the replacement ofthe typically polysilicon gate electrode with a metal gate electrode toimprove device performance with the decreased feature sizes. One methodof forming the metal gate electrode is a “gate last” or “replacementgate” methodology where a dummy gate, typically polysilicon is replacedby a metal gate. Providing the metal gate later in the process can avoidproblems of the stability of the work function metal during processing.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a perspective view of an embodiment of a FinFET deviceaccording to some embodiments of the disclosure.

FIG. 2A to FIG. 2J illustrate different steps of a method of forming aFinFET device according to some embodiments of the disclosure, in whichFIG. 2A to FIG. 2E are perspective views and FIG. 2F to FIG. 2J arecross-sectional views.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The present disclosure relates generally to semiconductor components,such as a FinFET device and method of fabricating a FinFET device orportion of a device. There has been a desire to replace the gate oxideand polysilicon gate electrode with a high-k gate dielectric and metalgate electrode to imp rove device performance as feature sizes continueto decrease. A gate last (or gate replacement) approach has beenimplemented to address concerns of high temperature processing on metalmaterials. However, challenges are raised in providing an appropriatestress and/or gate resistance in devices such as metal gate FinFETs. Forexample, low stress on the gate and/or high gate resistance can cause adegradation of performance of device. Therefore, there is a need tobalance the stress and/or gate resistance in devices such as metal gateFinFETs, such that the gate leakage and/or work function can beimproved.

FIG. 1 is a perspective view of an embodiment of a FinFET deviceaccording to some embodiments of the disclosure. The FinFET device 100includes a substrate 102. In some embodiments, the substrate 102includes a bulk silicon substrate. The substrate 102 may be silicon in acrystalline structure. In other embodiments, the substrate 102 mayinclude other elementary semiconductors such as germanium, or include acompound semiconductor such as, silicon carbide, gallium arsenide,indium arsenide, and indium phosphide. In some other embodiments, thesubstrate 102 includes a silicon-on-insulator (SOI) substrate. The SOIsubstrate may be fabricated using separation by implantation of oxygen,wafer bonding, and/or other suitable methods.

The FinFET device 100 further includes fin structures 104, 106 (e.g., Sifins) that extend from the substrate 102. In some embodiments, the finstructures 104, 106 may optionally include germanium. The fin structures104, 106 may be fabricated by using suitable processes such asphotolithography and etch. In some embodiments, the fin structures 104,106 are etched from the substrate 102 using dry etch or plasmaprocesses. Shallow trench isolation (STI) structures 108 surround thefins 104, 106. The STI structures 108 may include any suitableinsulating material. It is understood that although two fin structuresare illustrated, additional parallel fins may be formed in a similarmanner.

The FinFET device 100 further includes a gate structure 110. The gatestructure 110 is formed on a central portion of the fin structures 104,106. In some embodiments, multiple gate structures are formed over thefin structures. The gate structure 110 includes a gate dielectric layerand a gate electrode. It is understood that numerous other layers mayalso be present, for example, capping layers, interface layers, spacerelements, and/or other suitable features. In some embodiments, the gatedielectric layer may include an interfacial layer such as silicon oxide.The gate dielectric layer may further include other dielectric materialssuch as, silicon nitride, silicon oxinitride, dielectric with a highdielectric constant (high-k), and/or combinations thereof. Examples ofhigh-k dielectric materials include hafnium oxide, zirconium oxide,aluminum oxide, hafnium dioxide-alumina alloy, hafnium silicon oxide,hafnium silicon oxynitride, hafnium tantalum oxide, hafnium titaniumoxide, hafnium zirconium oxide and/or combinations thereof. The gateelectrode may include polysilicon and/or a metal including metalcompounds such as, TiN, TaN, NiSi, CoSi, Mo, Cu, W, Al, Co, and/or othersuitable conductive materials. The gate electrode may be formed in agate last process (or gate replacement process) as will be explainedbelow.

The fin structures 104, 106 include a channel region 112 surrounded bythe gate structure 110. The fin structures 104, 106 may be doped toprovide a suitable channel for an N-type FinFET (NMOS device) or P-typeFinFET (PMOS device). The fin structures 104, 106 may be doped usingprocesses such as, ion implantation, diffusion, annealing, and/or othersuitable processes. The fin structures 104, 106 include a source region114 and drain region 116 associated with the FinFET device 100. Thesource region 114 and drain region 116 may include an epitaxial (epi)silicon (Si) or epi silicon carbide (SiC) for an NMOS device, and episilicon germanium (SiGe) or epi germanium (Ge) for a PMOS device. TheFinFET device 100 may be a device included in a microprocessor, memorycell (e.g., SRAM), and/or other integrated circuits.

FIG. 2A to FIG. 2J illustrate different steps of a method of forming aFinFET device according to some embodiments of the disclosure, in whichFIG. 2A to FIG. 2E are perspective views and FIG. 2F to FIG. 2J arecross-sectional views. In FIG. 2A, a semiconductor substrate isprovided. The semiconductor substrate can be a silicon-containingsubstrate 200 with multiple fin structures 202 extending in a firstdirection. Thereafter, an insulating layer 204 is formed to fill thelower portions of gaps between the fin structures 202 as STI. Thematerial of the insulating layer 204 can be, but is not limited to,silicon oxide. The method of forming the insulating layer 204 includesdepositing an insulating material layer on the substrate 200 coveringthe fin structures 202, optionally performing a planarization process tomake insulating layer 204 flat, and then performing an etch back processuntil the upper portions of the fin structures 202 are exposed. The finstructures 202 may include source regions, drain regions, and channelregions connecting the source regions and the drain regions.

Referring to FIG. 2B, an interfacial layer 206 is conformally formed onthe substrate 200 covering the fin structures 202. The interfacial layer206 includes silicon oxide, silicon nitride or silicon oxynitride. Theinterfacial layer 206 is formed by a deposition process, such as anatomic layer deposition (ALD) process, a chemical vapor deposition (CVD)process, a physical vapor deposition (PVD) process or a sputterdeposition process. It is noted that the interfacial layer 206 is formedby a deposition process rather than a thermal oxidation treatment.Silicon consumption due to the thermal oxidation treatment does notoccur, so that the shape of the fins 102 is not deformed during the stepof forming the interfacial layer 206. As shown in FIG. 2B, theinterfacial layer 206 is conformally formed along the surface of eachfin 202. In the present embodiment, since the interfacial layer 206 isformed by a deposition process without consuming any silicon, the shapeof the fin structures 202 keeps well-defined after the formation of theinterfacial layer 206.

Thereafter, a dummy gate material layer 208 and a mask layer 210 aresequentially formed on the interfacial layer 206. The dummy gatematerial layer 208 includes polysilicon. The mask layer 210 includessilicon oxide, silicon nitride, silicon oxynitride or a combinationthereof. Each of the dummy gate material layer 208 and the mask layer210 can be formed by a deposition process, such as an ALD process, a CVDprocess, a PVD process or a sputter deposition process. In FIG. 2B, asingle mask layer 210 is provided for illustration purposes, but thepresent disclosure is not limited thereto. In another embodiment, themask layer 210 can be a multi-layer structure including, for example, alower silicon nitride layer and an upper silicon oxide layer.

Referring to FIG. 2C, the mask layer 210, the dummy gate material layer208 and the interfacial layer 206 are patterned to form a stackedstructure 212 including the interfacial layer 206, the dummy gatematerial layer 208 and the mask layer 210 sequentially formed on thesubstrate 200. The stacked structure 212 crosses the fin structures 202and extends in a second direction different from the first direction. Insome embodiments, the second direction is perpendicular to the firstdirection. The patterning step includes performing photolithography andetching processes.

Referring to FIG. 2D, a spacer 214 is formed beside the stackedstructure 212. The method of forming the spacer 214 includes forming asilicon oxide layer on the substrate 200 and then performing ananisotropic etching process to remove a portion of the silicon oxidelayer. Source and drain regions (see FIG. 1 ) are then formed in thesubstrate 200 beside the spacer 214. Thereafter, a contact etch stoplayer (CESL) 216 and an interlayer dielectric (ILD) layer 218 aresequentially formed on the substrate 200 to cover the stacked structure212. The CESL 216 includes silicon nitride. The ILD layer 218 includessilicon oxide, silicon nitride, silicon oxynitride, silicon carbide,low-dielectric constant dielectric material or a combination thereof.Each of the CESL 216 and the ILD layer 218 can be formed by a depositionprocess, such as an ALD process, a CVD process, a PVD process or asputter deposition process. Afterwards, a portion of the ILD layer 218and a portion of the CESL 216 are removed to expose the top of thestacked structure 212. The removing step includes performing a CMPprocess.

Referring to FIG. 2E, the stacked structure 212 is removed to form atrench 220 in the ILD layer 218. The removing step includes performingan etch back process. Note that the interfacial layer 206 can beregarded as a sacrificial layer since it is removed during the step ofremoving the stacked structure 212.

Referring to FIG. 2F, another interfacial layer 222 and a high-kdielectric layer 224, are sequentially formed at least on the surface ofthe trench 220. The interfacial layer 222 includes silicon oxide,silicon nitride or silicon oxynitride. The interfacial layer 222 isformed by a deposition process, such as an ALD process, a CVD process, aPVD process or a sputter deposition process. It is noted that theinterfacial layer 222 is formed by a deposition process rather than athermal oxidation treatment. Silicon consumption due to the thermaloxidation treatment does not occur, so that the shape of the finstructures 202 (see FIG. 2A) is not deformed during the step of formingthe interfacial layer 222. The interfacial layer 222 is conformallyformed along the surface of each fin 202. In the some embodiments, sincethe interfacial layer 222 is formed by a deposition process withoutconsuming any silicon, the shape of the fin structures 202 keepswell-defined after the formation of the interfacial layer 222.

The high-k dielectric layer 224 includes a high-k material with highdielectric constant. The high-k material can be metal oxide, such asrare earth metal oxide. The high-k material can be selected from thegroup consisting of hafnium oxide (HfO₂), hafnium silicon oxide(HfSiO₄), hafnium silicon oxynitride (HfSiON), aluminum oxide (Al₂O₃),lanthanum oxide (La₂O₃), tantalum oxide (Ta₂O₅), yttrium oxide (Y₂O₃),zirconium oxide (ZrO₂), strontium titanate oxide (SrTiO₃), zirconiumsilicon oxide (ZrSiO₄), hafnium zirconium oxide (HfZrO₄), strontiumbismuth tantalate, (SrBi₂Ta₂O₉, SBT), lead zirconate titanate(PbZr_(x)Ti₁-xO₃, PZT), and barium strontium titanate (Ba_(x)Sr₁-xTiO₃,BST), wherein x is between 0 and 1. The high-k dielectric layer 224 isformed by a deposition process, such as an ALD process, a CVD process, aPVD process or a sputter deposition process.

Thereafter, a composite metal layer 236 is formed on the substrate 200to at least fill up the trench 220 (shown in FIG. 2E) as a stacked metalgate. The composite metal layer 236 is formed filling the trench 220.The composite metal layer 236 includes, from bottom to top, a barrierlayer 240, a work function metal layer 242, and a metal gate 244.

The barrier layer 240 is formed on and capping the high-k dielectriclayer 224. The barrier layer 240 can be a metal layer, such as atitanium nitride (TiN) layer. The barrier layer 240 can be formed by adeposition process, such as an ALD process, a CVD process, a PVD processor a sputter deposition process. The barrier layer 240 can also beformed by a nitridation process, such as using a thermal chemical vapordeposition reaction between ammonia (NH₃) and titanium tetrachloride(TiCl₄). In some embodiments, the surface of the barrier layer 240 canbe further treated by a nitridation process, such as using ammonia gas.Alternatively, in some embodiments, a post metal anneal (PMA) processcan be utilized to improve the density and the quality of the high-kdielectric layer 224 and the barrier layer 240.

The work function metal layer 242 is formed on the barrier layer 240. Insome embodiments, the FinFET device can be a NMOS device, and the workfunction metal layer 242 can be made of, for example, Ti, Ag, Al,TiAlMo, Ta, TaN, TiAlC, TiAlN, TaC, TaCN, TaSiN, Mn, Zr, or combinationsthereof. Alternatively, the FinFET device can be a PMOS device, and thework function metal layer 242 can be made of, for example, TiN, W, Ta,Ni, Pt, Ru, Mo, Al, WN, or combinations thereof. The work function metallayer 242 can be formed by a deposition process, such as an ALD process,a CVD process, a PVD process or a sputter deposition process.

The metal gate 244 is formed on the work function metal layer 242. Themetal gate 244 is deposited on the work function metal layer 242 by ALD,PVD, CVD, or other processes. The metal gate 244 is made of, forexample, Al, W, Co, Cu.

In FIG. 2F, the interfacial layer 222, the high-k dielectric layer 224,and the composite metal layer 236 protruding from the ILD layer 218(e.g. portions outside the trench 220) are removed. The FinFET device isthus obtained, wherein the high-k dielectric layer 224 serves as a gatedielectric layer, and the composite layer 236 serves as a metal gateelectrode. The removing step can be performed by a CMP process.

After the surface of the FinFET device is flattened, there is a need toremove a portion of the interfacial layer 222, the high-k dielectriclayer 224, and the metal gate 244 at the top in order to form adielectric cap thereon. The dielectric cap is utilized to space themetal gate 244 from conductive circuits lying above. The removing stepincludes using etch back process.

However, the CMP slurry is an aqueous solution including suspensions,such as silica, alumina, ceria abrasive, oxidizers, polymers, pHstabilizers, dispersants, and surfactants. Those suspensions may bediffused into the metal gate 244 during the CMP process. The diffusedportion of the metal gate 244 may occur etch back failure, which mayimpact SAC window and yield.

The present disclosure further includes applying a treatment to themetal gate 244, such that the etch back failure caused by diffusion canbe prevented. The treatment includes applying a reduction gas to themetal gate 244, as shown in FIG. 2G to FIG. 2J, which are partialcross-sectional views of the semiconductor component according to someembodiments of the disclosure.

In FIG. 2G, the reduction gas 250 is led into the processing chamber.The reduction gas 250 is in contact with the metal gate 244. Thereduction gas 250 includes reducing gas, which can react with thediffused suspensions in the metal gate 244. The reducing gas 250 has theability to reduce the diffused suspensions (cause them to gainelectrons). The reducing gas 250 is said to be reductive or reducing.The reducing gas 250 transfers electrons to the diffused suspensions,and is thus itself oxidized. Meanwhile, the diffused suspensions is saidto be oxidative or oxidizing and can be known as oxidizing agents. Thatis, the diffused suspensions remove electrons from the reducing gas 250,and is thus itself reduced.

In some embodiments, the diffused suspensions may be the organiccompounds or the diffused suspension may include chlorine. Accordingly,the reducing gas 250 has the ability to reduce carbon and chlorine. Thereducing ability relates to redox potential (also known as reductionpotential, oxidation/reduction potential) of the substance. Redoxpotential is a measure of the tendency of a chemical species to acquireelectrons and thereby be reduced. Reduction potential is measured involts (V), or millivolts (mV). Each species has its own intrinsic redoxpotential; the more positive the potential, the greater the species'affinity for electrons and tendency to be reduced.

However, the metal gate 244 is also made of the material which is ableto be oxidized. Therefore, the redox potential of the reducing gas 250need to be considered and cannot be too high in order to not to oxidizethe metal gate 244 simultaneously when the diffused suspensions arereduced. In some embodiments, the metal gate 244 can be made of, forexample, Al, W, Co, or Cu. The redox potential of the reducing gas 250is greater than that of the compound of carbon or chlorine but is notgreater than that of Al, W, Co, or Cu.

In some embodiments, the reducing gas 250 is a gas including hydrogenwith dilute gas, such as N₂/Ar/He inert gas. The reducing gas caninclude H₂N₂. The reducing gas 250 may involve the use of hydrogen gaswith a catalyst. These catalytic reductions are used primarily in thereduction of carbon-carbon bonds.

The processing chamber and the substrate 200 are further heated. In someembodiments, the processing chamber can be heated by applying opticaltechniques (tungsten filament lamps, lasers), thermal radiationtechniques, or by using susceptors and radio frequency (RF) inductionheating. The reducing gas 250 in the processing chamber is also heatedand becomes high-temperature reducing gas 250, and the high-temperaturereducing gas 250 is of a temperature in a range from about 200° C. toabout 400° C. The hydrogen, including hydrogen atom and hydrogen ion,may penetrate into the metal gate 244. The hydrogen is able to reducethe diffused suspensions, such as compounds of carbon and/or chlorine,such that the diffused suspensions from the CMP slurry would not affectthe following processes applying to the metal gate 244. In someembodiments, the reduction of carbon, such as organic compounds and/orreduction of chlorine (e.g. compounds of chlorine, such as Al(Cl)_(x) orW(Cl)_(y)) can be observed in the metal gate 244 after the reducingprocess.

Referring to FIG. 2H. the top portion of the metal gate 244 is removed.The removing step includes performing etch back processes. In someembodiments, the removing step involves introducing an etchant into theprocessing chamber and reacting the etchant with the metal gate 244, inwhich the etchant has high selectivity between the metal gate 244 andthe work function metal layer 242. The temperature may be selected basedon etchant chemical composition, a desired etching rate, and othermaterial and process parameters. In some embodiments, the etchant usedin the etch back process is a fluorine based etchant, such as nitrogentrifluoride (NF), fluorine (F₂), tetrafluoromethane (CFO),tetrafluoroethylene (C₂F₄), hexafluoroethane (C₂F₆), octafluoropropane(C₃F₈), sulfur hexafluoride (SF), and others. In some embodiments, whenthe fluorine based etchant is utilized, the substrate is heated to arange between about 300° C. and 450° C. Other temperature ranges may beused for different types of etchants. The etchant may be introduced intothe processing chamber from the remote plasma generator to provideactivated species (including radicals, ions and/or high energymolecules). Flow rates of the etchant typically depend on a size of thechamber, etching rates, etching uniformity, and other parameters.

Referring to FIG. 2I, the top portion of the work function metal layer242 is removed after the metal gate 244 is etched back. The etchingprocess may implement etchant different from that of etching the metalgate 244. The etchant utilized to remove the work function metal layer242 also has high selectivity between the work function metal later 242and the metal gate 244. In some embodiments, the etchant may bechlorine-based etchant, such as chlorine (Cl₂), trichloromethane(CHCl₃), carbon tetrachloride (CCl₄), and/or boron trichloride (BCl₃),bromine-containing gas, such as hydrogen bromide (HBr) and/ortribromomethane (CHBr₃), iodine-containing gas, other suitable gasesand/or plasmas, and/or combinations thereof.

The metal gate 244 and the work function metal layer 242 are two-stepetched to gain high etching selectivity. The metal gate 244 is protrudedfrom the work function metal layer 242. Namely, the height of the metalgate 244 is greater than that of the work function metal layer 242. Insome embodiments, the distance between the top surface of the metal gate244 and the work function metal layer 242 is in a range from about 1 nmto about 5 nm.

Referring to FIG. 2J, a dielectric layer 260 is formed on and cappingthe metal gate 244 and the work function metal layer 242. The dielectriclayer 260 fills the trench 220. The dielectric layer 260 includessilicon oxide, silicon nitride, silicon oxynitride, silicon carbide,low-dielectric constant dielectric material or a combination thereof.The dielectric layer 260 can be formed by a deposition process, such asan ALD process, a CVD process, a PVD process or a sputter depositionprocess. Afterwards, a portion of the dielectric layer 260 protrudingfrom the trench 220 (shown in FIG. 2E) is removed. The removing stepincludes performing a CMP process. The top surface of the dielectriclayer 260, the ILD layer 218, and the CESL 216 are substantially at thesame level, such that the semiconductor component, e.g. the FinFETdevice may provide a flatten top surface for forming circuits thereon,and the dielectric layer 260 is utilized to isolate the circuit and themetal gate 244.

By inducing the reducing gas into the processing chamber, the diffusedsuspensions in the metal gate can be reduced, such that the etch backprocess to the metal gate can be performed successfully.

In an embodiment, a semiconductor device includes: a semiconductor finextending from a substrate; a gate dielectric layer extending alongsides and over a top surface of the semiconductor fin; a work functionmetal layer over the gate dielectric layer, a topmost surface of thework function metal layer being beneath a topmost surface of the gatedielectric layer; a metal gate over the work function metal layer, atopmost surface of the metal gate being beneath the topmost surface ofthe gate dielectric layer and being above the topmost surface of thework function metal layer; and a dielectric layer over the metal gateand the work function metal layer, a topmost surface of the dielectriclayer being planar with the topmost surface of the gate dielectriclayer.

In some embodiments of the semiconductor device, a portion of thedielectric layer is laterally disposed between the metal gate and thegate dielectric layer. In some embodiments, the semiconductor devicefurther includes: a barrier layer disposed between the work functionmetal layer and the gate dielectric layer. In some embodiments of thesemiconductor device, the dielectric layer contacts sides of the metalgate and the barrier layer. In some embodiments of the semiconductordevice, the metal gate includes: a conductive material having a firstredox potential; and suspensions diffused in the conductive material,the suspensions having a second redox potential when the suspensions areoxidized, the second redox potential being less than the first redoxpotential. In some embodiments of the semiconductor device, thesuspensions include carbon. In some embodiments of the semiconductordevice, the suspensions further include chlorine.

In an embodiment, a semiconductor device includes: a semiconductor finextending from a substrate; gate spacers on the semiconductor fin; agate dielectric layer over a top surface of the semiconductor fin, thegate dielectric layer extending along sides of the gate spacers; a workfunction metal layer over the gate dielectric layer; and a metal gateover the work function metal layer, the metal gate including aconductive material and suspensions diffused in the conductive material,the suspensions in an upper region of the metal gate being oxidizedsuspensions, the suspensions in a lower region of the metal gate beingreduced suspensions.

In some embodiments of the semiconductor device, the suspensions includecarbon. In some embodiments of the semiconductor device, the suspensionsfurther include chlorine. In some embodiments of the semiconductordevice, the conductive material has a first redox potential and theoxidized suspensions have a second redox potential, the second redoxpotential being less than the first redox potential. In some embodimentsof the semiconductor device, the metal gate further includes a reducingmaterial diffused in the conductive material, the reducing materialhaving a third redox potential, the third redox potential being greaterthan the second redox potential and less than the first redox potential.In some embodiments of the semiconductor device, the reducing materialincludes hydrogen.

In an embodiment, a semiconductor device includes: an interlayerdielectric (ILD) layer having a trench; a metal gate formed in thetrench; a work function metal layer formed between the metal gate andthe trench, where a height of the metal gate is greater than that of thework function metal layer; and a dielectric layer formed on the metalgate and the work function metal layer.

In some embodiments of the semiconductor device, top surfaces of thedielectric layer and the ILD layer are substantially at the same level.In some embodiments of the semiconductor device, a height of the metalgate is less than that of the ILD. In some embodiments of thesemiconductor device, a portion of the dielectric layer is laterallydisposed between the metal gate and the ILD. In some embodiments of thesemiconductor device, the metal gate includes: a conductive materialhaving a first redox potential; and suspensions diffused in theconductive material, the suspensions having a second redox potentialwhen the suspensions are oxidized, the second redox potential being lessthan the first redox potential. In some embodiments of the semiconductordevice, the suspensions include carbon. In some embodiments of thesemiconductor device, the suspensions further include chlorine.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a fin extending froma substrate; forming a dummy gate over a channel region of the fin;forming a source/drain region adjacent the dummy gate; depositing aninterlayer dielectric (ILD) layer over the source/drain region;replacing the dummy gate with a metal gate, the metal gate comprising afirst metal; planarizing the metal gate and the ILD layer with achemical mechanical polish (CMP) process, suspensions of a slurry forthe CMP process being diffused into the first metal of the metal gateduring the CMP process, the suspensions comprising carbon; and after theplanarizing, exposing the metal gate to a reducing gas, the reducing gaspenetrating into the first metal of the metal gate to react with thesuspensions of the slurry diffused into the first metal of the metalgate, a redox potential of the reducing gas being greater than a redoxpotential of the suspensions, a redox potential of the first metal beinggreater than the redox potential of the reducing gas, the reducing gascomprising H₂N₂.
 2. The method of claim 1, wherein the suspensionsfurther comprise chlorine.
 3. The method of claim 1 further comprising:after exposing the metal gate to the reducing gas, recessing the metalgate; forming a dielectric layer on the metal gate; and planarizing thedielectric layer and the ILD layer.
 4. The method of claim 3, whereinreplacing the dummy gate with the metal gate comprises forming a workfunction metal layer, the metal gate is formed on the work functionmetal layer, and recessing the metal gate comprises: removing a firsttop portion of the metal gate with a first etching process; and removinga second top portion of the work function metal layer with a secondetching process.
 5. The method of claim 4, wherein after the secondetching process, a height of the metal gate is greater than a height ofthe work function metal layer and less than a height of the ILD layer.6. A method comprising: depositing a conductive material in a trenchbetween gate spacers; planarizing the conductive material with achemical mechanical polish (CMP) process to form a metal gate in thetrench, suspensions of a slurry for the CMP process being diffused intothe conductive material of the metal gate during the CMP process, thesuspensions having a first redox potential, the conductive materialhaving a second redox potential; reducing the suspensions in theconductive material of the metal gate with a reducing process, areducing gas for the reducing process having a third redox potential,the third redox potential being greater than the first redox potential,the third redox potential being less than the second redox potential,the reducing gas being diffused into the conductive material of themetal gate during the reducing process; and recessing the metal gatewith an etch back process.
 7. The method of claim 6, wherein depositingthe conductive material in the trench comprises: depositing a barrierlayer in the trench; depositing a work function metal layer on thebarrier layer; and depositing a layer for the metal gate on the workfunction metal layer, the layer for the metal gate formed of theconductive material.
 8. The method of claim 7, wherein the etch backprocess comprises: etching the metal gate with a first etchant; andetching the work function metal layer with a second etchant, the secondetchant being different from the first etchant.
 9. The method of claim8, wherein the suspensions comprise carbon, the reducing gas compriseshydrogen gas, the first etchant is a fluorine-based etchant, and thesecond etchant is a chlorine-based etchant.
 10. The method of claim 9,wherein the suspensions further comprise chlorine.
 11. The method ofclaim 8, wherein after the etch back process, a first height of the gatespacers is greater than a second height of the metal gate, and thesecond height of the metal gate is greater than a third height of thework function metal layer.
 12. The method of claim 6 further comprising:after the etch back process, depositing a dielectric layer on the metalgate; and planarizing the dielectric layer and the gate spacers.
 13. Themethod of claim 6 further comprising: forming the gate spacers adjacenta dummy gate, the dummy gate surrounding a channel region; and removingthe dummy gate to form the trench.
 14. The method of claim 6, whereinthe reducing gas comprises H₂N₂.
 15. A method comprising: removing adummy gate structure to form a trench between gate spacers; depositingmetal layers in the trench; planarizing the metal layers with a chemicalmechanical polish (CMP) process to form a metal gate structure fromportions of the metal layers remaining in the trench, suspensions of aslurry for the CMP process being diffused into a main metal layer of themetal layers during the CMP process; after planarizing the metal layers,treating the metal gate structure with a processing gas, the processinggas penetrating into the main metal layer to react with the suspensionsof the slurry diffused into the main metal layer, the processing gasbeing a reducing agent for the suspensions, the suspensions being anoxidizing agent for the processing gas, wherein a redox potential of theprocessing gas is greater than a redox potential of the suspensions andless than a redox potential of a metal of the main metal layer; aftertreating the metal gate structure, etching back the metal gate structureto form a recess, wherein treating the metal gate structure preventsetch back failure caused by diffusion of the suspensions into the mainmetal layer; and forming a dielectric layer in the recess.
 16. Themethod of claim 15, wherein the processing gas is not an oxidizing agentfor the metal layers.
 17. The method of claim 15, wherein depositing themetal layers in the trench comprises: depositing a barrier layer in thetrench; depositing a work function metal layer on the barrier layer; anddepositing the main metal layer on the work function metal layer. 18.The method of claim 17, wherein the suspensions comprise carbon, theprocessing gas comprises hydrogen gas, and etching the metal gatestructure comprises: etching the main metal layer with a fluorine-basedetchant; and etching the work function metal layer with a chlorine-basedetchant.
 19. The method of claim 18, wherein the suspensions furthercomprise chlorine.
 20. The method of claim 15, wherein the processinggas comprises H₂N₂.